It has been proposed (e.g., in U.S. Pat. No. 6,863,220) to include a user-actuated switch in a proximity payment card so that the card may be in an unactivated state except when the user actuates the switch while presenting the card for reading by a point of sale terminal. By requiring a user to actuate a switch in order to activate the card, it may be possible to prevent certain attacks on the security of the card account number. Such attacks may occur by surreptitiously reading the card from a distance while the card is in the holder's purse or wallet.
A possible disadvantage of proposed designs for a proximity payment card having a user-actuatable switch is that the resulting cards may be unduly expensive to manufacture.